Abstract

The Upper Pliocene Kalogeros cryptodome is exposed on the northeastern part of Milos, Greece. The dacite
cryptodome is 800-1300 m across and at least 120 m high. It is inferred to have intruded wet, unconsolidated
pumiceous sediments in a shallow marine environment. The Kalogeros cryptodome includes five facies. The coherent
dacite facies (80 vol%) consists of massive, non-vesicular dacite and is characterised by radial columnar joints 20-250
cm across. The banded dacite facies (15 vol%) encircles the coherent core and is up to 40 m thick. It comprises
alternating bands (0.5-4 m thick) of pale grey and black dacite. The fractured dacite facies (less than 1 vol%) forms an irregular zone (1-3 m thick) at the outer margin of the cryptodome. The outermost massive dacite breccia facies ( less than 2 vol%) consists of blocky to polyhedral dacite clasts (1-40 cm in diameter) and is characterised by domains of jigsawfit and clast-rotated breccia. The stratified dacite breccia (2vol%) is clast-to-matrix supported, monomictic, poorly sorted and composed of dacite clasts up to several metres in diameter. The facies association collectively records endogenous growth of a cryptodome that involved a continuous magma supply during a single intrusive phase and simple expansion (inflation). During emplacement, the margins of the Kalogeros cryptodome were quench fragmented, forming an outer domain of intrusive hyaloclastite and intensely fractured dacite. The near-solid outer carapace insulated the hotter, less viscous interior. Laminar shear accompanied inflation, generating large-scale flow banding around the outer part of the core. Once stagnant, concentric isotherms were established within the cryptodome and controlled the orientation of columnar joints. Cryptodomes are characterised by a well-developed internal concentric distribution of distinctive textural domains, modest autoclastic breccia, and the absence of redeposited autoclastic facies.